CONVERTED BACHMANN 2-6-0                                              TRUCK  CONVERSION                                                                      SOUND DECODER CONVERSION

FINISHED MODEL                                                                        TENDER TOP INSERT / TRUCKS / TOOLBOXES (2 spares)

N-407 Bachmann 2-6-0 ATSF 9446 tender conversion 3D printed

History.

ATSF Mogul 2-6-0 9446 started life as engine number 23 on the Fort Worth & Rio Grande branch of the St.Louis & San Francisco Railroad.

Santa Fe acquired the branch and its engines on 3-1-1937. It was rebuild in Cleburne and renumbered 2446, 02445 and finally 9446.

It was scrapped 7-22-1947.

Building instructions.

The Bachmann 2-6-0 is a fine running engine. It is available DCC equipped as ATSF 9446 and is (in my opinion) a good starting point for a conversion to a passable copy of the real thing. Overall dimensions and contour of the engine and lower part of the tender are within acceptable margins. The model has a couple of obvious differences from the original, of which some can be easily corrected.  After conversion one rather noticable issue remains: the driver spacing (which is incorrectable) and also the running boards are a little different.

The benefit is that i(f you want to convert to sound) there is just enough room in the tender to apply a Soundtraxx Econami-100 Steam and also backup lighting.

You can have a good running and pulling small sound-equipped (reasonable) Santa Fe prototype engine for a decent price.

This conversion focusses on 4 aspects: the valve gear, the tender shell, the tender trucks and the decoder.

The valve gear on the model is Walschaert and should be Stephenson, I choose not to 3D print a new cylinder block because the model has the gear parts permanently attached to it. With care and patience I started to grind the round contoured upper piston valve to a square Stephenson look alike slide valve box, using my motor tool and finishing the job with small fine files. Of course you have to disassemble the front of the engine first (little screw front underside and the two little screws in the main driver. Frequently check the contour and inside of the plastic cylinder block to keep everything as square as possible and the wall thickness just enough. Because it will be repainted black slight imperfections will not attrack too much attention.

You also have to grind off the steam chests on both sides of the metal shell plus the first part of the running board. Using a grinding disk in your motor tool work very slowly and frequently check the contour of the shell and pictures of the original and model.

Only the front of the smokebox should be tarpon gray: using an airbrush repaint the sides of the smokebox black, conceiling the bare metal visible after the grinding job.   

The tender shell on the original model is a coal bunker wheras the prototype ran on oil. In my Shapeways Shop you can find a drop-in oil tender top,  Archbar trucks and tool boxes. Disassemble the tender by removing the shell. It takes quite a bit of force to disengage the latching bulges halfway the long sides. Using a cutting disk remove the side boards above the level of the back part of the tender. Also remove the rear deck of the tender where the water intake is located. Sand/file the sides carefully to the level of the top rear part of the tender. Also file the inside surface of all sides of the tender shell smooth, leaving the latching bulges in places. The 3D printed Frosted Extreme Detail oil tank insert is a perfect drop-in now. 

There are 4 small holes in the top of the 3D printed tenderdeck. Taking some scrap 0,3 brass (or other metal) wire bend the 2 U formed handrails (one 4,5 mm legs apart, the other 7,5 mm legs apart). Insert from above and glue from underside with some ACC; top/horizontal bar should be 4 mm above deck.

The tender trucks are next. Remove the wheelsets and the metal contact strips from the original trucks and reverse the process on the 3D printed Archbar trucks. The brass contact strips have to be adjusted a little: grind away a little on the upper side of the horizontal bar (near the vertical bar) to assure a good flat fit and if you want to install a sound decoder shorten the vertical bar by about 2 mm (see picture above). Also file/grind the outside top of this vertical bar to create a clean brass soldering spot for the wire. After inserting the contact strip through the hole in the truck Insulate the soldering spot with a short piece of shrink tubing (in this case discard the plastic insert/mounting pad for the silent decoder).

DO NOT USE TOO MUCH FORCE TO REINSTALL THE WHEELSETS INTO THE TRUCK FRAMES (the 3D material is more brittle than the original plastic/nylon trucks and might break. You should have to spread the truck frame only a little bit to replace the wheel sets. To achieve this it might be necessary to grind a little bit off the cones of the wheelsets, The wheelsets should have some room/play between the contact strips to avoid excessive drag. Also check/adjust the gauge of the wheelsets (the factory setting is a bit narrow).

The trucks are designed to lower the tender a bit. On the front truck this happens automatically (using the original drawbar). On the rear truck there are two small metal pins on the underside of the frame to keep the truck level. You will have to grind about 1 mm off these pins, keeping them level. Grind a little at a time and holding the trucks in place check the space between truck and tender frame of front and rear truck: it should be equal. This way you will lower the rear coupler a bit but the top side will still be level with a Micro Trains coupler gauge: adjust the trip pin a little.

Remove (grind away) the large air reservoir in the middle of the underside of the truck frame. Using a little styrene shIm (level with the underside of the side sill of the tender frame) install the 2 tool boxes on the underside of the tender floor in the middle between the trucks using a little drop of ACC.

One can use the original DCC decoder (which is OK but simple) but because the tender top is a little higher now then it was before there is also the possiblity of installing a Soundtraxx Econami-100 Steam sound decoder. Carefully remove the black wires from the original decoder one by one, color coding them directly (red=right pickup, black = left pickup, gray = - motor lead, orange = + motor lead, white = forward lamp, blue = common). To create more room in the tender discard the plastic insert together with the long contact strips. I shortened the 4 vertical truck contact strips to the top level of the metal underframe, soldered short flexible black wires to them before reassembling the trucks, same wire gauge as the decoder wires) and isolated them from the metal tenderframe using short pieces of shrink tubing. This way the decoder sits lower, right between the truck power pickups, creating enough room for the speaker in the tender top and wire connections and resistors alongside the decoder. Use a sugarcube speaker glued to a piece of styrene that fits inside the top of the oil tank. The air chamber is quite small but the sound will be quite good (walls are sturdy). Do not forget to insert the top handrails first and glue them carefully from the inside to plug the holes in the airchamber. There is even enough room for a SMD led plus 470 Ohm resistor for the backup light. Also put a 470 Ohm resistor in the white front light lead. The capacitor will fit in the back of the tender. Be careful to use the smallest possible pieces of shrink tubing on all connections.

Painting and decalling.

If you work very carefully you only have to paint the oil tender insert and tender trucks using an airbrush. Be sure to clean the 3D prints very carefully. Soak them in GooGone or Bestine for 24 hours and wash afterwards in soapy water, Let them dry completely. The valve gear can be painted by hand. Redecalling is not even necessary.

Programming the decoder using JMRI is quite simple, especially synchronising the exhaust to the wheel revolutions.

Enjoy your little sound equipped Mogul.